Strip tensioning apparatus



Jan. 9, 1968 P. A. GAY 3,362,202

' STRIP TENSIONING APPARATUS Filed June 25, 1965 5 Sheets-Sheet 1 11 j56.2 r I Z? 1 [2. I m 5 4 8 e2 -C/ 5 4 3 2 m m 172 m m J 1 5: 5/ A/ 5 6a! a a,

Jan. 9, 1968 J P. A. GAY 3,362,202

' STR-IP TENSIONING APPARATUS Filed June 25, 1965 I I 3 Sheets-Sheet 211 g 17 l8 19" W P. A. GAY

Jan. 9, 1968 3 Sheets-Sheet 3 Filed June 25, 1965 J Hill! W JY 2 T T z/r W v A h 2 a1 ,v I. I|.|| a 0 Z k United States Patent ABSTRACT OF THEDISCLOSURE An apparatus designed to place metallic strips undercontinuous tension formed by rollers separated into two sets. One ofsaid sets driving while the other brakes the strip passing between therollers. Each of the rollers of the sets for braking and driving withthe exception of one of the rollers of the braking set and one of therollers of the driving set begin provided with a slip coupling to permita slipping under a regulatable predetermined cou pling, for example apowder-magnetic type coupling.

In sheet metal working plants it is often required to subject sheet andstrip material to elongation and tension. This may be necessary forvarious purposes, such as planishing the sheet, or performing any ofvarious operations on the sheet while in a state of tension, includinginter alia alternate flexing of the tensioned sheet for simultaneouslyplanishing and cold-working it, light rolling of the tensioned sheet ina skinpass roll mill, and the like.

Strip-tensioning apparatus as used for the above purposes generallycomprises two sets of rollers rotatable on parallel, e.g. horizontal,axes. The rollers in both sets are so disposed that a strip to betensioned can be passed over a sinuous path around the rollers of afirst set in frictional engagement with opposite surface arcs of saidrollers, and then in similar fashion around the rollers of the otherset. The rollers of one set, the one situated foremost along thedirection of strip travel, are driven to feed the strip in thatdirection, while the rollers of the other, rearmost, set are driven incorresponding directions but at slightly lower velocities, or arebraked, so as to impose a retarding force on the strip. In this mannerthe strip can be placed under substantial elastic tension in the regionbetween the two sets of rollers.

In any strip-tensioning process, the important factor generally is thedegree of elongation imparted to the strip rather than the tension forcedeveloped therein. It is the degree of elongation percent, rather thanthe tension, that is directly related to the basic mechanicalcharacteristic of the strip material, including elastic limit andtensile yield point. It is, consequently, important that during a striptensioning process means be available for accuracy controlling theactual degree of elongation of the strip. Strip-tensioning machines ofthe prior art have been deficient in this respect. As will be latershown in detail, su h conventional machines are so constructed that theymust be operated to determine a certain value of tension, notelongation, in the sheet, or alternatively, it operated to impose aprescribed degree of elongation, they inevitably result in considerableslippage between the strip and the roller surfaces, causing damage tothe surface condition of the sheet to a degree that is intolerable inmany applications.

Objects of the present invention include the provision of improvedsheetand strip-tensioning apparatus and improved drive and controlsystems therefor, possessing some or all of the following advantages:

The actual elongation in the strip imparted during the tensioningprocess is controllable to within close tolerances, in a simple andreliable manner.

Strip elongation can be maintained at any accurately prescribed valueover a broad range without subjecting the strip to substantially anyslippage against the roller surfaces.

The full capacity of the power plant is at all times utilized formaximum efiiciency and economy of the process.

The process is readily controllable through manual and/ or automaticmeans in order to vary the elongation and tension imparted to the stripwhile retaining optimal slipfree operation.

The drive system is simple and economical, requiring only a single primemover to power all the rollers of both sets, and the entire system isreversible.

Other objects and advantages will appear. An exemplary embodiment of theinvention will now be described for purposes of illustration but not oflimitation with referrence to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view in elevation illustrating the principel ofa strip-tensioning process;

FIG. 2 is a simplified plan view showing an improved strip-tensioningapparatus according to the invention;

FIG. 3 diagrammatically shows a set of rollers of the apparatus andserves to indicate certain quantities involved in the determination ofthe torque settings to be used in the slip couplings employed in theinvention;

FIG. 4 is a circuit diagram of a control circuit usable in controllingthe apparatus of the invention; and

FIG. 5 is a diagrammatic view, partly in plan and partly in circuitschematic form, illustrating one form of automatic control usable in theapparatus of the invention.

In the diagrammatic view of FIG. 1 the general operating principle ofany strip-tensioning apparatus is illustrated. Such apparatus basicallyincludes two spaced sets of rollers a a and b b so disposed that a strip1 can be fed over a sinuous path in frictional engagement with mutuallyopposed surface portions of successive rollers in each set. Assuming thedirection of strip travel is to be leftward as indicated by arrows, thenthe rollers of the foremost group b b are all rotated to impart thisdirection of feed to the strip. It will be clear that for this purposethe upper rollers b b and 11., should be rotated counterclockwise andthe lower rollers b and [2 clockwise.

The rollers of the rearmost group a -a are operated to impose aretarding force to the strip 1. For this purpose, generally speaking,the rollers a a may be driven in the same directions as thecorresponding rollers in the set b b but at slightly slower speeds toimpart the desired retarding force, or said rollers ti -a may havebraking torques applied thereto with generally similar results.

Under these conditions, it will be evident that the strip 1 will besubjected to tension and consequent elongation in the straight lap ofits path of travel between rollers a and b Any desired strip-workingmachine may be interposed in this section, such as a rolling mill, analternate bending device, or any other machine serving to work the stripwhile in its tensioned and elongated condition.

In the past, two broad classes of power drive systems have beenavailable for powering the rollers of such strip-tensioning apparatus.In a first class, the rollers in each of the two sets il -L1 and b b maybe geared together for rotation at corresponding angular speeds, and thetwo sets may be driven from a common motor or separate motors at therequisite differential speeds, with the group b rollers being driven inthe same directions as but slightly slower than the group a rollers toimpart the desired retarding force to the strip.

Such systems are advantageously simple, and they have a furtherimportant advantage in that they make it possible accurately andreliably to control the actual degree of elongation sustained by thestrip between the two sets of driving and retarding rollers. Theelongation is proportional to the speed differential between the twosets of rollers, and since the rollers are positively driven the speeddifference is well determined and accurately controllable. However, sucha drive system has had a very serious drawback in that slippagenecessarily occurs between the strip and at least some of the rollers ineach set.

The reason for this slippage is that the tension present in the strip isnot uniform throughout the apparatus, but varies from a minimum at apoint ahead of the foremost retarding roller a to a maximum between theoutput retarding roller (1 and input driving roller b and then back to aminimum value beyond the output roller b of the driving set. The tensionincreases in increments as the strip moves past each of the retardingrollers a, and decreases again in increments as the strip moves pasteach of the driving rollers b. Due to these incremental variations instrip tension, as imparted by each successive roller, it is evident thatthe strip must slip relative to the roller surface by the amountrequired to take up the difference in tension across the roller. Suchslippage seriously damages the surface condition of the strip.

In an attempt to overcome this difficulty, a minor variation of theconventional drive system just described has involved impartingincrementally varying diameters to the successive rollers in each set,the diameters being increased from a to 6 and then decreased from 12 tob so as to cause corresponding incremental variations in the peripheralvelocity of the rollers for taking up the aforementioned incrementalvariations in tension and thereby prevent slippage. Such a knownarrangement, however, is capable at best of preventing slippage for onespecific set of operating conditions, i.e. for one type of stripmaterial (which determines the friction coefficient) one size of strip(determining the area of frictional contact), and one type of processingapplied to the tensioned strip (determining the maximum tension of thestrip). The arrangement therefore does not really solve the statedproblem.

The other class of conventional power drive system referred to above hasconsisted in connecting each of the driving rollers b b to an individualdrive motor, and each of the retarding rollers (1 to an individualbraking generator or equivalent braking device. This of course makes itpossible to proportion the driving and retarding torques applied to theindividual rollers in such a way as to eliminate slippage completely.However, another serious difficulty is introduced. Since in such asystem it is the torque, rather than the velocity, of each roller thatis positively determined by the system, the apparatus when thus drivenwill operate to impart a determined tension to the strip rather than adetermined elongation. In view of the practicably unavoidable variationsin the thickness and other characteristics of the strip material, itthen becomes difficult or impossible to impart the precise desired valueof elongation to the strip, which elongation values are of course in allcases very small. As stated above, the important factor to be consideredwhen working a sheet or strip under tension, is the precise value of itselongation.

The invention completely eliminates the above deficiencies of prior artstrip-tensioning apparatus by providing an improved drive and controlsystem for the rollers, as will now be described with reference to FIG.2.

This figure shows in plan view the set of retarding rollers (l -a andthe set of driving rollers b b Mounted on the shafts c of the retardingrollers a -a respectively in a manner later described, are meshing gearsal -d and mounted on the shafts of the driving rollers 12 -12 aremeshing gears e -e As here shown all the gears are substantiallyidentical. Preferably however gear d has a pitch diameter slightlysmaller than that of gears d d and gear e has a pitch diameter slightlylarger than that of gears b -b As a result, it will be noted that rollera imparts substantially no additional increment of tension to the stripand roller [1 imparts substantially no decrement of tension.

The input gear c of the driving roller set is driven through bevelgearing fi-g from the output shaft of a motor h. The motor output shaftis connected with the input gear of a differential gearing i, shown as aconventional bevel-gear epicyclic train, and the output of thisdifferential, by way of a further bevel gearing g f drives the gear dassociated with the output roller of the retarding set.

To adjust the velocity differential between the input and output of thedifferential 1', means are provided for controlling the rate of rotationof the spider of the differential, and as shown a worm gear k secured onthe spider meshes with a worm j, which may be driven from any suitablemeans such as conventional speed variator .not shown.

In the drive shaft 0 of each of the rollers of both sets other than theoutput retarding roller a and input driving roller b a torque-limitingcoupling device In is interposed. The devices in may be any suitabletype of torque limiter or slip clutch capable of automatic disengagementwhen the torque through it exceeds a prescribed, adjustable, value.Preferably slip couplings m are of the powdermagnetic type disclosed inFrench Patents 973,367 and 988,971, wherein the limiting torque issubstantially proportional to the energizing current applied to awinding of the coupling.

In the operation of this apparatus, it will be obvious that with themotor h revolving in an appropriate direction (in the present instanceclockwise as looking leftward from the outer end of the motor shaft),all of the rollers of the driving set b b will be rotated throughgearing g -f in the requisite directions to feed the strip 1 leftward asindicated with reference to FIG. 1. If differential spider i is heldstationary then it can easily be seen that the rollers of the retardingset a a are also driven in the same directions as the correspondingdriving rollers (l -(l and at the same speeds as they.

If now the differential spider i is rotated in a suitable direction at aslow rate by way of its control input j, then the forward angularvelocity of the retarding rollers a a will be decreased by acorresponding small amount, and said rollers will exert the desiredretarding force upon the strip. It may be noted in this connection sheetthe disclosed embodiment is reversible. In that strips can be fedthere-through in either direction, and either of the two sets of rollerscan be made to act as the driving set, or as the retarding set, merelyby reversing the sense of rotation of the differential input j.

The elongation undergone by the strip in the straight lap betweenrollers a and [1 is proportional to the difference between theperipheral velocities of said two rollers. Hence, any desired degree ofelongation can be accurately imparted to the strip by suitablycontrolling the angular velocity imparted to differential spider i.

At the same time, the system makes it possible to impart the desiredelongation to the strip without subjecting the strip to relativeslippage over any of the rollers of either set, ti -a or [l -b For thispurpose, the slip clutches m are preset so that each clutch willdisengage for a particular, determinable value of the torque transmittedthrough it.

It will be realized that as earlier indicated the tension present in thestrip 1 at different points of its path through the apparatus is notuniform. This tension is at a minimum, say t ahead of the input roller aof the retarding set, then increases in increments as the strip movespast each successive retarding roller, from t to t (across roller althen from t to 1 (across roller a and so on up to a maximum value t just'beyond the roller a No additional tension is imparted across the outputroller a This maximum tension 1 is maintained in the straight lap of thestrips path and across the input roller b of the driving set. Thereafterthe tension again decreases in increments, from L, to t;, (across rollerb and so on until it is restored to a value which generally issubstantially the initial value t beyond the output driving roller 11 Inview of these incremental variations in strip tension along its path, itis apparent that if the rollers in each group were positively driventhrough their positively intermeshing gears, various amounts of slippagewould inevitably have to occur between the strip and the various rollersof each set in order to take up the differences in tension. The need forstrip slippage is avoided through the provision of the slip couplings mof the invention, each clutch yielding as required to take up thedifference in strip tension produced across the associated roller.

In accordance with a feature of the invention, the torque values forwhich the various slip couplings m are set to yield, are predeterminedin each case so as to result in the minimum amount of slippage requiredto take up the difference in tension, and thereby utilize the drivecapacity of motor h to a maximum degree.

For this purpose, the said preset yield torque of each slip coupling mis made somewhat less, by a safety coefiicient somewhat less than unity,than the theoretical value of the torque required to be applied to theparticular roller under consideration in order to generate thecorresponding incremental variation in the tension of the strip as thestrip moves past said roller. This may be clarified as follows.

Considering FIG. 3, the five rollers I to V there shown may beconsidered as constituting, for example, the retarding rollers a a Ifthe initial tension of the strip ahead of the input roller is t anddesignating by t t t t the successive tension values in the strip asmeasured immediately beyond the rollers :1 a a in, then the theoreticalvalues of the retarding torques which the rollers would have to apply inorder to produce the incremental tension variations are In theseexpressions C C C C are the torques applied by the retarding rollers andR is the common roller radius.

From the mechanics of friction, it is known that each of the tensionvalues t t t I is related to the preceding tension value by thefollowing equations where f is the friction coefiicient of the strip onthe roller surface, the alphas are the winding angles of the striparound the rollers (see FIG. 3), and e is the base of naturallogarithms.

From the above Equations 1 and 2, and introducing the above-mentionedsafety coefficient 1, the following set of expressions can be writtenfor the yield torques to be preset in the respective slip couplings ofeach set:

It is to be noted that the initial tension t can, if desired, beexpressed in terms of the final tension L; by applying the relations(2).

Knowing the geometry of the system and the characteristic frictioncoetficient of the strip material being processed, the above torquevalues C C C C can easily be calculated in each particular instance, andthe slip couplings of each roller set a and b can then be preset inaccordance with the calculated values to provide optimal operation,wherein: (a) a prescribed degree of elongation can be accuratelyimparted to the strip by controlling the rate of rotation of thedifferential spider i, (b) the strip will be free of any damagingslippage during its contact with any of the rollers, and (c) the powerinput of the system is utilized with maximum efiiciency.

As earlier noted, conveniently the slip couplings used are of the typewherein the yield torque is proportional to the energizing currentapplied to the coupling. In such cases all the slip couplings of eachset are advantageously controlled through a common current controlcircuit such as the one shown in FIG. 4. In this circuit 13, 14, 15, 16represent the energizing windings of the four slip couplings m,connected in series with related variable resistors or potentiometers17, 18, 19, 20. The four series combinations are connected in parallelacross a pair of energizing lines connected by way of a generaladjustment potentiometer 12 with a constant current source 11. It willbe evident that with this circuit arrangement the resistors 1720 can beindividually adjusted in accordance with the torque values as computedfrom Equations 3, whereby the desired operation will be obtained.According to a further aspect of the invention, means are provided forautomatically varying the values of the energizing current for the slipcouplings m of each set in accordance with the tension applied to thestrip, while maintaining said current values at all times proportionalto the optimal yield torque values as determined by Equations 3.

The usefulness of this aspect of the invention arises from the fact thatthe effective final tension of the strip in the section thereof betweenthe retarding rollers a and driving rollers b may vary, as when saidstrip is for example subjected to rolling bending or other operations inits said intermediate section. The precise value of said final tension(t and hence that of the initial tension (t may be difficult todetermine, and may vary during a given process. The embodiment of theinvention now to be described maintains the correct values for the yieldtorques of the slip couplings, as defined above, regardless of suchvariations in tension.

For this purpose, in the embodiment now to be described with referenceto FIG. 5, the torque applied to the rigidly mounted roller of either(or each) set, i.e. the output roller a of the retarding set or/ and theinput roller b of the driving set, is measured directly on the rollershaft, as by means of a strain-gauge or other suitable torque-measuringdevice. The resulting torque signal which is a measure of the finaltension present in the strip beyond roller 12;, or ahead of roller b isapplied as a control signal to vary the energizing currents to the slipcouplings, without altering the proportionality relationshipstherebetween.

In the specific example of such an arrangement shown in FIG. 5, theleft-hand shaft 0 represents either of the rigidly coupled shafts inFIG. 2, e.g. the shaft carrying the output retarding roller a Atorque-measuring device is illustrated as an assembly of fourstrain-gauges n bonded to a surface of the shaft between the roller anddrive gear, and arranged in a balanced bridge circuit having its one (orinput) diagonal connected by way of slip-rings O with a voltage sourceshown as including a DC source u and potentiometer p. The other (output)diagonal of the strain-gauge bridge circuit is connected to sliprings 0for providing an output voltage signal proportional to the torsionalstrain of the shaft as sensed by the strain gauges.

The output signal is applied to a first differential amplifier 11 whichhas one of its inputs connected to one of the sliprings 0 directly, andits other input connected to the other slipring 0 by way of a voltagesource a" and potentiometer p", for conventional balancing purposes.

Connected with the output of amplifier n are four potentiometers inparallel, p 7 1 2 only 2 being shown in the drawing. These fourpotentiometers are respectively associated with the energizing windingsof the four slip couplings In.

One of said slip couplings is shown at m in FIG. 5 mounted on itsrelated shaft (cg. one of shafts u n, in FIG. 2), and only theconnection of this slip coupling with its potentiometer will bedescribed, it being understood that similar circuits are provided inrespect to the other three slip couplings and related otentiometers.

Potentiometer 17 has its resistance terminal remote from the terminalconnected to amplifier n grounded, and has its adjustable tap connectedto one input of a further difierential amplifier q The output ofamplifier q is connected to one input of a suitable firing circuit 1,having its other input grounded. The firing circuit 1 has a pair ofoutputs connected with the control electrodes of respective controlledrectifier diodes r. The diodes r have terminals of similar denominationconnected to the ends of the secondary winding of a supply transformer,whose primary is connected across an A-C supply. The other terminals ofcontrolled diodes r are connected in common to a slipring O, which isconnected with one end of the energizing winding, not shown, of slipcoupling m. The other end of said energizing winding is connectedthrough another slipring O to ground.

A midtap of the secondary of the supply transformer is connected througha shunt resistor s to ground, and is also connected to the second inputof differential amplifier q to provide a stabilizing feedbackconnection.

In the operation of this circuit, a voltage signal from the strain gaugedevice, representative of the torque of the rigid shaft of roller (1 andhence the final tension in the strip, is applied, after amplification in12 to all four potentiometers p 12 11 p, in parallel. A portion of thisvoltage signal, as determined by the setting of each said potentiometer,is applied through amplifier 1 to firing circuit t. The firing circuitoperates to control the rectifier diodes in proportion with the voltageapplied to its input, and the rectifiers apply unidirectional current ofaccurately regulated intensity from the supply transformer to thecontrol winding of slip coupling in.

It will be understood that the circuit just described is but oneconvenient means of applying precisely regulated current to all fourslip clutches m, proportional to the torque strain sensed in the shaftof the rigid roller a or b while maintaining at all times between thecurrents applied to the respective slip clutches the accuratelypredetermined relations given by Equations 3 above. These relations aswill be understood, are predetermined by the settings of thepotentiometers p 2 p and 12 The strip tensioning apparatus of theinvention, as herein disclosed, has many important advantages oversimilar apparatus equipped with drive means of the prior art. Accuratelycontrolled elongations can be imparted to strips with a degree ofprecision which was not heretofore achievable without at the same timesubjecting the strips to objectionable slippage and surface shear.Controlling the roller drive so as to maintain strip elongation, ratherthan strip tension, constant, as made possible by the invention, makesit feasible and safe to planish metal sheets by subjecting them toelongations just short of the yield point of the metal, in cases wherethe elastic limit and yield point are quite close to each other, as incertain light alloys. Accurate control of the elongation is alsoimportant in skin-pass operations since the cold working involved insuch processes depends directly on the amount of elongation rather thantension imparted.

Various modifications may be introduced into the embodiment shown anddescribed without exceeding the scope of the invention. Thus, while thedifferential gearing shown provides a preferred means for imparting thedesired differential angular velocities to the positively driven rollersof the respective sets, other positive drive means capable of drivingsaid rollers at the desired speeds may be used. Also, the yieldinglydriven rollers, rather than all being geared with one another and withthe positively driven rollers, may be connected with the source ofmechanical power through other forms of drive transmission, providedthese include the yielding connections or slip-couplings which form anessential feature of this invention.

While it is essential according to the invention that there is a rollerin each set which is positively driven, in order to produce anaccurately determinable elongation in the strip corresponding to thedifference in the drive velocities of said positively driven rollers, itis not essential that said positively driven rollers constitute theoutput roller of the retarding set and the input roller of the drivingset.

What is claimed is:

1. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over asinuous path in frictional engagement with the roller surface of firstone then the other set;

positive drive means connected for rotating a roller in each set ataccurately determinable different speeds so as to feed said strip pastsaid sets while imposing a prescribed elongation to the strip asdetermined by the difference in said speeds; and

other drive means connected for rotating the remaining rollers saidother drive means including yielding connections, whereby said remainingrollers will participate in feeding and tensioning the strip in aSubstantially slip-free manner.

2. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over asinuous path in frictional engagement with the rollers of first one thenthe other set; a source of mechanical power; a positive drive connectionfrom the power source to a roller of one of the sets;

differential gearing having an input connected to be positively drivenfrom the power source and having an output connected for positivelydriving a roller of the other set, and having another input rotatable toimpart a selectable speed differential to the speeds of said positivelydriven rollers; and

drive means connected for rotating the remaining rollers from the powersource, and including yielding connections whereby said remainingrollers will participate in feeding and tensioning the strip in asubstantially slip-free manner.

3. The apparatus defined in claim 2, including a gear fixedly connectedwith each of said positively-driven rollers, and further gears connectedby way of said yielding connections with each of the remaining rollers,said further gears being in meshing relationship with one another andwith the respectively associated first-mentioned gears.

4. Strip tensioning apparatus comprising:

two sets of rotatable rollers arranged to have a strip fed over asinuous path in frictional engagement with the rollers of first one thenthe other set;

a source of mechanical power;

positive drive means connected to the power source for rotating a rollerin each set at determinable different speeds so as to feed the strippast said sets while imposing a prescribed elongation to the strip asdetermined by the difference in said speeds; other drive means connectedto the power source for rotating the remaining rollers of both sets; and

slip coupling means interposed in said other drive means connected toeach said remaining roller, including means for individually setting themaximum value of transmitted torque in each of said slip coupling means.

5. The apparatus defined in claim 4, including means for simultaneouslyvarying said maximum transmitted 9 torque values in all of said slipcoupling means while maintaining said values proportional to presetquantities. 6. The apparatus defined in claim 4, including means sensingthe tension in a strip, means connected with the 10 8. The apparatusdefined in claim 1, wherein said positively driven rollers comprise anoutput roller of said first set and an input roller of said second set.

9. The apparatus defined in claim 1, wherein each of sensing means andwith each of said slip coupling means 5 said positively driven rollersis slightly smaller in difor simultaneously varying said maximumtransmitted torque value in all of said slip coupling means inproportion to the sensed strip tension, and means for maintaining thesaid values proportional to preset quantities.

7. The apparatus defined in claim 4, including means sensing the torquedeveloped in one of said positivelydriven rollers, means connected withsaid sensing means and with each of the slip coupling means forsimultaneously varying said maximum transmitted torque value in all ofsaid slip coupling means in proportion to the sensed torque, and meansfor maintaining said values proportional to preset quantities.

ameter than the diameter of the remaining rollers of the related set.

References Cited UNITED STATES PATENTS 1,943,005 1/1934 Coryell 722052,287,380 6/1942 Klein et a1. 72-205 2,526,296 10/1950 Stone 72205 15RICHARD J. HERBST, Primary Examiner.

R. D. GREFE, Assistant Examiner.

